� GANDHI INSTITUTE FOR EDUCATION AND TECHNOLOGY� (NAAC Accredited A+ Grade Engineering college)� Baniatangi , Bhubaneswar, Khordha -752060� (Approved by AICTE & Govt of Orissa , Affiliated to BPUT & SCTE&VT

Course

Analog Electronics

&

Opamp

Program- Diploma in Electrical Engineering

Semester- 4th

� Semiconductor

• Semiconductors are the materials which have a conductivity between conductors (generally metals) and non-conductors or insulators (such as ceramics).
• Example- Si, Ge, GaAs etc.

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� PN junction diode

• When a p-type semiconductor is suitably joined to n-type semiconductor, the contact surface is called p-n Junction.
• The positive and negative uncovered charge produces an electric field across the pn junction. The direction of this electric field is from n side to p side. This electric field set up by the uncovered charges in the pn junction diode is called the Barrier Field or Barrier potential.
• The typical barrier potential is approximately: - For Si, V₀ = 0.7 V, For Ge, V₀ = 0.3 V.

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BREAKDOWN VOLTAGE: - It is the minimum reverse voltage at which pn junction

breaks down with sudden rise in reverse current.

KNEE VOLTAGE: - It is the forward voltage at which the current through the junction

starts to increase rapidly.

Forward and Reverse biasing of PN diode

• CLIPPING CIRCUITS

The circuit with which the waveform is shaped by removing (or clipping) a portion of the applied wave is known as a clipping circuit. The important diode clippers are:-

• 1. Positive clipper and negative clipper
• 2. Biased positive clipper and biased negative clipper
• 3. Combination clipper.

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• CLAMPER CIRCUITS:-

A clamping circuit is used to place either the positive or negative peak of a signal at a desired level. The dc component is simply added or subtracted to/from the input signal.

The clamper is of two types :-

• 1. Positive clamper
• 2. Negative clamper

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• SPECIAL SEMICONDUCTOR DEVICES

THERMISTOR-

 Thermistor is the contraction of the term Thermal Resistor.It is generally composed of semiconductor materials. Most thermistors have a negative coefficient of temperature that is their resistance decreases with the increases of temperature.

Applications-

 It is used for measurement and control of temperature and for temperature compensation.

 It is used for measurement of power at high frequency. It is also used for thermal

conductivity.

• BARRETERS
•  Barreters are the short length wires with fine diameters with operating range around 150⁰C.
• SENSORS
•  A sensor is a device that detects events or changes in quantities and provides a corresponding output, generally as an electrical or optical signal; for example, a thermocouple converts temperature to an output voltage. Sensors are used in everyday objects such as touch-sensitive elevator buttons and lamps which dim or brighten by touching the base, besides innumerable applications of which most people are never aware.

• ZENER DIODE:-
•  A properly doped crystal diode which has a sharp breakdown voltage is known as a Zener Diode. A Zener diode is always reverse connected i.e. it is always reverse biased. Zener diode operated in this region will have a relatively constant voltage across it, regardless of the value of current through the device. This permits the Zener diode to be used as a Voltage Regulator.

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PIN DIODE:-  The PIN diode is a PN junction with an intrinsic layer between the P and N layers. The intrinsic layer of the PIN diode is a layer without doping, and as a result this increases the size of the depletion region i.e the region between the P and N layers where there are no majority carriers.

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• TUNNEL DIODE:-
• A Tunnel diode is a heavily doped p-n junction diode in which the electric current decreases as the voltage increases.
• In tunnel diode, electric current is caused by “Tunneling”. The tunnel diode is used as a very fast switching device in computers. It is also used in high-frequency oscillators and amplifiers.

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� Half-wave Rectifier

Half-wave rectifiers transform AC voltage to DC voltage. A halfwave rectifier circuit uses only one diode for the transformation. A halfwave rectifier is defined as a type of rectifier that allows only one-half cycle of an AC voltage waveform to pass while blocking the other half cycle.

• FULL WAVE RECTIFIER
• In full-wave rectification, current flows through the load in the same direction for both half-cycles of input A.C. voltage. This can be achieved with two diodes working alternately.

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COMPARISION OF HALFWAVE AND FULL WAVE RECTIFIERS

• FILTER CIRCUITS:-
• A filter circuit is a device which removes the A.C. component of rectifier output but allows the D.C.component to reach the load. A filter circuit is generally a combination of inductors (L) and capacitors (C).
• Types Of Filter Circuits:- 

The most commonly used filter circuits are : - Inductive Filter or Series Inductor,  Capacitor Filter or Shunt Capacitor,  Choke Input Filter or LC Filter and Capacitor Input Filter or π-Filter.

• BIPOLAR JUNCTION TRANSISTORS

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• A transistor consists of two PN junctions formed by sandwiching either p-type or n-type semiconductor between a pair of opposite types. Hence Transistor is classified into two types, namely: - 
• (i) n-p-n transistor (ii) p-n-p transistor
• The section on one side is the emitter and the section on the opposite side is the collector. The middle section is called the base and forms two junctions between the emitter and collector.
• It has three terminals- emitter , base and collector.

• TRANSISTOR CONFIGURATION

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• TRANSISTOR BIASING:-
• To achieve faithful amplification the following basic conditions must be satisfied:-

(i) Proper zero signal collector current

(ii) Minimum proper base-emitter voltage (V_BE) at any instant

(iii) Minimum proper collector-emitter voltage (V_CE) at any instant

• STABILITY FACTOR :-  The rate of change of collector current I_C w.r.t. the collector leakage current I_CO at constant β and I_B is called stability factor
• METHODS OF TRANSISTOR BIASING:-

(i) Base resistor method

(ii) Biasing with collector-feedback resistor

(iii) Voltage-divider bias

Base resistor method

• The biasing circuit shown by has a base resistor R_B connected between the base and the V_CC. Here the base-emitter junction of the transistor is forward biased by the voltage drop across R_B which is the result of I_B flowing through it.
• Here the values of V_CC and V_BE are fixed while the value for R_B is constant once the circuit is designed. This leads to a constant value for IB resulting in a fixed operating point due to which the circuit is named as fixed base bias. This kind of bias, results in a stability factor of (β+1) which leads to very poor thermal stability.

• Collector to base bias
• This circuit helps in improving the stability considerably. If the value of I_C increases, the voltage across R_L increases and hence the V_CE also increases. This in turn reduces the base current I_B.
• S<(β+1)

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• Voltage divider biasing
• Among all the methods of providing biasing and stabilization, the voltage divider bias method is the most prominent one. Here, two resistors R₁ and R₂ are employed, which are connected to V_CC and provide biasing. The resistor R_E employed in the emitter provides stabilization.
• S=1

The DC load line is the load line of the DC equivalent circuit, defined by reducing the reactive components to zero (replacing capacitors by open circuits and inductors by short circuits).

• Q-point- It is the steady-state DC voltage or current at a specified terminal of an active device such as a diode or transistor with no input signal applied.

• TRANSISTOR AMPLIFIERS

• h-parameter representation is widely used in modeling of electronic components & circuits, particularly transistors.
•  As both short circuit & open circuit terminal conditions are utilized hence, this parameter representation is known as hybrid parameter representation.

• MULTI STAGE TRANSISTOR AMPLIFIER:-
• A transistor circuit containing more than one stage of amplification is known as multistage transistor.
• Gain: - The ratio of the output electrical quantity to the input one of the amplifier is called its gain.The gain of a multistage amplifier is equal to the product of gains of individual stages.
• Frequency response: - The curve between voltage gain and signal frequency of an amplifier is known as frequency response.
• Bandwidth: - The range of frequency over which the voltage gain is equal to or greater than 70.7% of the maximum gain is known as bandwidth.

• FREQUENCY RESPONSE OF R-C COUPLED TRANSISTOR AMPLIFIER:
• (i) At low frequencies (< 50 Hz):- The voltage gain decrease due to CC and CE capacitors.
• (ii) At high frequencies (> 20 kHz): The voltage gain reduces due to internal capacitances and junction capacitances.
• (iii) At mid-frequencies (50 Hz to 20 kHz):- At this stage the voltage gain of the amplifier is constant.

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• Feedback-
• The phenomenon of feeding a portion of the output signal back to the input circuit is known as feedback.
• Feedback is of two types.
• Positive Feedback
• Negative Feedback

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• Positive or regenerate feedback:
• • In positive feedback, the feedback energy (voltage or currents), is in phase with the input signal and thus aids it.

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• Negative or Degenerate feedback:
• In negative feedback, the feedback energy (voltage or current), is out of phase with the input signal and thus opposes it. The phenomenon of feeding a portion of the output signal back to the input circuit is known as feedback.
• Negative feedback reduces gain of the amplifier. It also reduce distortion, noise and instability.
• This feedback increases bandwidth and improves input and output impedances.
• Due to these advantages, the negative feedback is frequently used in amplifiers.

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• POWER AMPLIFIER
• The function of a power amplifier is to raise the power level of input signal. It is required to deliver a large amount of power and has to handle large current.

ClassificationBasedonFrequencies

• Power amplifiers are divided into two categories, based on the frequencies they handle. They are as follows.
•  Audio Power Amplifiers − The audio power amplifiers raise the power level of signals that have audio frequency range (20 Hz to 20 KHz). They are also known as Small signal power amplifiers.
•  Radio Power Amplifiers − Radio Power Amplifiers or tuned power amplifiers raise the power level of signals that have radio frequency range (3 KHz to 300 GHz). They are also known as large signal power amplifiers.

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• Classification -Based on Mode of Operation
• On the basis of the mode of operation, i.e., the portion of the input cycle during which collector current flows, the power amplifiers may be classified as follows.
•  Class A Power amplifier − When the collector current flows at all times during the full cycle of signal, the power amplifier is known as class A power amplifier.
•  Class B Power amplifier − When the collector current flows only during the positive half cycle of the input signal, the power amplifier is known as class B power amplifier.

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• Class B push-pull amplifier

Circuit diagram Output waveform

• Oscillators
• An electronic device that generates sinusoidal oscillations of desired frequency is known as a sinusoidal oscillator.

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• Barkhausen criterion-

1.The loop gain is equal to unity in absolute magnitude, that is, | β A | = 1 and

2. The phase shift around the loop is zero or an integer multiple of 2π radian (180°) i.e.<β.A = 0

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• RC PHASE SHIFT OSCILLATOR-
• RC phase shift oscillator using op-amp in inverting amplifier introduces the phase shift of 180º between input and output. The feedback network consists of 3 RC sections each producing 60º phase shift. The output of amplifier is given to feedback network. The output of feedback network drives the amplifier. The total phase shift around a loop is 180⁰ and 180⁰ due to 3RC sections, thus 360 º. This satisfies the required condition for positive feedback and circuitworks as an oscillator.

• Hartley Oscillator/ Tank circuit:
•  A LC oscillator which uses two inductive reactance and one capacitive reactance in its feedback network is called Hartley oscillator. CE amplifier provides a phase shift of 180⁰ and LC feedback network provides additional 180⁰ phase shift. The resistance R1 and R2 are the biasing resistances. The RFC is the radio frequency choke. Its reactance value is very high frequencies; hence it can be treated as open circuit. While for d.c conditions, the reactance is zero hence cause no problem for d.c capacitors. Hence due to RFC, the isolation between a.c. and d.c operation is achieved.

• COLPITT OSCILLATOR
• A Colpitts oscillator looks just like the Hartley oscillator but the inductors and capacitors are replaced with each other in the tank circuit.

• WIEN BRIDGE OSCILLATOR
• The Wien Bridge Oscillator uses two RC networks connected together to produce a sinusoidal oscillator.The Wien Bridge Oscillator is so called because the circuit is based on a frequency-selective form of the Wheatstone bridge circuit. The Wien Bridge oscillator is a two-stage RC coupled amplifier circuit that has good stability at its resonant frequency.

• FIELD EFFECT TRANSISTOR
• A Field Effect Transistor (FET) is a three-terminal semiconductor device. Its operation is based on a controlled input voltage.
• Two types of FET-
• JFET & MOSFET
• JFET is of two types-

n channel JFET

p channel JFET

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• Working of n-channel JFET
• The working of JFET can be explained by discussing about how to turn on N-channel JFET and how to turn off N-channel JFET. For turning ON a N-channel JFET, positive voltage of V_DD has to be applied to the drain terminal of the transistor w.r.t (with respect to) source terminal such that the drain terminal must be appropriately more positive than the source terminal. Thus, current flow is allowed through the drain to source channel. If the voltage at the gate terminal, V_GG is 0V, then there will be maximum current at the drain terminal and N-channel JFET is said to be in ON condition.

• Transfer and drain characteristics of JFET

• Common source JFET Amplifier

A_V=-g_m(R_D//r₀)

• Common drain JFET Amplifier

A_V=g_mR_s/(1+g_mR_s)

• OPAMP
• An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output.

Equivalent circuit of opamp

• Characteristics of ideal opamp
• Infinite open-loop gain
• Infinite input impedance Rin, and so zero input current.
• Zero input offset voltage.
• Infinite output voltage range.
• Infinite bandwidth with zero phase shift and infinite slew rate.

• Inverting amplifier Non-inverting amplifier

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OPAMP Configurations

• Voltage follower

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• Summing circuit

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• Differential amplifier

Opamp as integrator and differentiator

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Opamp as comparator

Transfer characteristics of opamp

Thankyou